Modeling refers to the creation of a model from an object under design for describing the object to be manufactured. The development of data processing systems and computers has converted modeling into a computerized process, wherein a product model is created from the object. The product model of a building is the whole composed of the product data of the life span of the building and the building process. The product model of a building describes the product data of the building outlined in accordance with a product data model. The product model of a building may be stored as a database of a computer application or as a file suitable for data transfer. Computer applications describe the real-world building elements of the building using corresponding building element entities processed by the applications.
When modeling takes place by computer applications, two different approaches to modeling are in use: bottom-up and top-down. Bottom-up is developed from the requirements of the bulk industry and mechanics design to model individual pieces as flexibly and accurately as possible, wherein an independent model is created from individual parts and, if the final object comprises a plurality of parts, the model of the object is composed of the models of the individual parts by combining them together suitably. Top-down is developed from the requirements posed by the construction industry and other such industrial sectors, wherein large, differently hierarchical, unique objects composed of up to dozens of thousands of parts have to be designed and manufactured, wherein one product model is created from the entire object, whereby the building elements know that they belong to an entirety, and management of the entirety of the building is considerably easier than in the aforementioned bottom-up modeling. These modeling methods should not be mixed up with techniques employed in the processing of what are known as libraries for facilitating the processing: depending on the direction of movement, the movement in the hierarchy tree of a library is often also referred to as the top-down method (movement from the root of the hierarchy tree to the nodes) and the bottom-up method (movement from the nodes to the roots). However, these library movement methods do not correspond to the methods employed in modeling, although the names employed are the same.
In the construction industry and other industrial sectors, elements and objects have to be designed with limitless variations in appearance and product data. To manage this multiformity, parametric modeling has been taken into use in bottom-up modeling, wherein the modeler is able to create new building elements by storing parametric elements in a so-called library. In parametric modeling, the physical characteristics of an object are not programmatically fixed to the modeled object, but the physical characteristics are defined by giving the object different attributes as parameters, on the basis of which the geometry, i.e. the shape, of the modeled object is created. Since parameters may be created for the object without programming and since the size, shape and product data of the object can be changed by means of the parameters, the changing of a parametric object is quite simple. Owing to parametricity, objects modeled by copying the same object can also be changed by changing the librarized element.
In parametric modeling systems, the modeling of a column, for example, is initiated by searching the library, wherein column elements of different shapes are defined in advance (FIG. 1), for a column element fulfilling the correct details. FIG. 1 shows a small sample of a column library required when 0 to 3 beams are connected to a column. If the desired column element is found in the library, it is selected, values are assigned to the parameters of the column element, and the column thus created is added as part of the model and stored in a memory. The column is then part of the model. If the column is to be changed, for instance if one beam more or fewer is connected to the column than was assumed during the creation of the column, the library is searched for a column element according to the correct detail. If it is found, the data on the old column are deleted from the model, the new column element is selected, values are assigned to the parameters of the column element, the column is added as part of the model, and stored in a memory. The model then comprises a new kind of column. If a suitable column element is not found in the library when the column is created into the model for the first time or later when being changed, a new column element has to be defined in the library. The problem in this modeling method is that the library has to include a library element including the correct details, whereby the size of the library becomes large, thus complicating its use, requiring extremely much of the librarization system, and consuming memory resources, even if a hierarchical librarization system were utilized. From the point of view of the modeler, it is problematic that the starting point of the design is not from a logical direction and the final ensemble should be anticipated at the very beginning of the design in order to avoid unnecessary and error-prone amendment later on. For example, when creating a column, one should know how many beams are to be connected to the column in order to be able to select the right column library element, i.e. column element.
In top-down modeling, the last mentioned problem does not exist, since the entirety is modeled first in top-down modeling, and then the parts of the whole etc. and lastly the details. In other words, in top-down modeling, the aforementioned multiformity requirement is achieved by dividing the building elements into smaller wholes, such as separate building elements, connections and details that are programmed as part of the modeling program. These smaller programmed wholes are combined to enable the creation of the most typical building elements in use. In prior art solutions, the whole is achieved by creating objects in the model from generic elements, which can be freely combined. For example, when creating a column, one does not know how many beams are connected to the column, for example. In top-down modeling, the generic elements and the connections between them are implemented by software, the problem being that it does not include parametricity; instead, all characteristics of the modeled objects have to be programmed into the modeling program. For example, if a given kind of connection type is required, which is not programmed, it cannot be made, but a so-called user's connection can be made at most, which cannot be parameterized. An additional problem is that the inheritance of the characteristics cannot be utilized in propagating the changed to several parts at the same time. This means that if the cross-section of a column is changed, for example, the modeler himself has to change the connection created with a user's connection to correspond to the changes of the column.
In several top-down modeling systems, new connections and details can be added by adding programmed parametric connections to the modeling system. In other words, the program library therein includes definitions of different connections and details, from which the modeler or the modeling program selects the correct connection on the basis of given rules depending on the beams and/or columns to be connected, for example. The problem in this solution is that each connection programmed in the modeling program increases the program library unnecessarily thus causing the aforementioned problems, impairing the manageability of the library, for example. A further problem is that parametricity exists only in pre-programmed connections.